There are anecdotal reports of interference from various electronic devices (including DVD players, which are currently allowed) and some simulation studies suggest that interference is theoretically possible. Airlines continue to enforce a no-phones policy using the same precautionary principle adopted by petrol stations. However, a 2011 poll found that three per cent of British holidaymakers had forgotten to turn off their mobile phone when they flew. That would mean almost 6.5 million switched-on phones flew that year, suggesting the risk is – at worst – very small.